1. Field of the Invention
The invention relates to the compression molding of tablets and the like and more particularly relates to excipients for use in compression molding and a process for preparing the excipients.
2. Brief Description of the Prior Art
When powder or granules are molded by compression, there are instances where the main ingredients to be molded are too small in quantity to be molded, or where the main ingredients are difficult to mold by compression. In those cases, a method has often been used in which compression molding is conducted after mixing the main ingredient with an inert substance which has good moldability. This inert substance with the required moldability is called the excipient. This method is often carried out in the production of pharmaceuticals, veterinary drugs, agricultural chemicals, food products and cosmetics and some other chemicals. Lactose, microcrystalline cellulose powder and calcium hydrogen phosphate have been widely used as the excipient.
However, difficulties exist in using these substances. For example, lactose has advantages of low cost and chemical inertness and gives compression moldings of high hardness, but of no disintegrability. For pharmaceuticals, veterinary drugs and agricultural chemicals, it is necessary for the molding to disintegrate in a relatively short time in water or in digestive juice. The molds using lactose as the excipient, usually don't disintegrate or require a long time for disintegration and frequently cannot be put to practical use. In order to overcome this disadvantage, disintegrants, such as starch, calcium carboxymethylcellulose and low-substituted hydroxypropyl methylcellulose etc., must be added in appropriate proportions.
However, adding disintegrants is complicated, because a suitable combination has to be selected from a vast number of possible combinations of main ingredients plus excipients plus disintegrants in various rations. Conventionally, determination of the formulation including selection of the type and proportion of disintegrant has depended on many tests, conducted by trial and error technique. This is costly and inefficient.
Microcrystalline cellulose powder has excellent properties as an excipient because it is chemically inert, and able to give moldings of relatively high hardness and good disintegration time. However, it has poor flowability which causes difficult handling. It cannot be poured smoothly into the mold. Moreover, microcrystalline cellulose powder is expensive.
Calcium hydrogen phosphate produces moldings with high hardness but it is an ionic substance which cannot be regarded as chemically inert. This means that the range of applications employing it is limited. In addition to this disadvantage, it gives moldings of poor disintegrability. Hence it is inconvenient for use in industry.
The method of the invention provides a process for preparing an excipient which eradicates all of the above-mentioned difficulties. In accordance with this invention there is provided an excipient which will give rise to moldings with excellent disintegratability and high hardness, and which is physiologically harmless, chemically inert, highly flowable and of low cost.